This invention relates to an electrical switch and more particularly to a finger-operated, snap-action switch of the type usable in and mounted to a keyboard of a typewriter or a teleprinter.
The wide variety of keyboard-mounted switches found in present day printers and typewriters are well known. Often such switches are somewhat complex and are not easily assembled. Such complexity adds to the cost of the unit in which the switches are placed and creates problems during repair or replacement. Accordingly, one object of the present invention is the provision of an electrical switch simpler than those currently in use which is easy to manufacture, easy to assemble, and which exhibits high reliability.
A typical prior art keyboard switch often includes a plunger which slides in response to the application of finger force thereto. The sliding of the plunger ultimately affects the operation of some sort of circuit energization facility, such as causing the engagement of a pair of electrical contacts or altering the capacitance between two members by moving them relatively to each other. One difficulty with many types of prior art switches is that they lack so-called tactile feedback. Specifically, the plungers in many such switches slide in a smooth uniterrupted motion in such a manner that the operator is hard put to tell whether or not operation of the circuit energization (facility) has taken place. Usually such operation has in fact, taken place, but it has been found that there is a psychological need on the part of an operator to have some sort of tactile feedback at the fingertips indicating this condition. Switches for providing such tactile feedback are often referred to as "snap-action" switches. Accordingly, another object of this invention is to provide a snap-action switch which generates efficient tactile feedback to the operator.
In many prior art keyboard switches, it is possible that the full finger force applied to the plugner via a finger-engageable key may ultimately be applied to the electrical contacts or the capacitive members which are operated by the plunger. This is often damaging to the contacts or members, or at least increases the possibility of failure in a short time. Accordingly, another object of the present invention is to provide a snap-action electrical switch for use in a keyboard, which is designed in such a manner that the full application of finger force to the contacts or capacitive is effectively prevented.
Also, the prior art contains references to numerous electrical switches in which the snap-action is derived from the use of a magnet or magnets. Specifically, the force applied to the key and thus to the plunger must exceed the magnetic attraction between the magnet and a movable armature before the plunger will move. The sudden breaking away of the armature from the magnet is what provides the so-called snap-action in the switches. However, many prior art devices are overly complicated as to the relationship of the magnet to other parts of the switch. Moreover, in assembly and use of such switches, precise alignment and positioning techniques must often be utilized to render them properly operative. Thus, another object of the present invention is to provide a magnetic, snap-action, electrical switch for use in a keyboard, which is easy to assembly, which is reliable, and which avoids the complication of the prior art by providing for a convenient and efficient association of the parts thereof in a single, durable unit.